The present invention relates to injection moldable blends of silicone copolymer and polyetherimide. The silicone copolymer has been found to enhance the properties of the polyetherimide in the resulting blend without significantly reducing the upper-use temperature of the polyetherimide.
Prior to the present invention, polyetherimide, such as shown by Heath et al., U.S. Pat. No. 3,847,867, assigned to the same assignee as the present invention and incorporated herein by reference, have been used in a variety of applications requiring a high performance injection moldable material and a T.sub.g of at least 200.degree. C. Although polyetherimides have exhibited superior solvent resistance, strength, and flame resistance, methods for improving such properties as greater oxygen plasma, and atomic oxygen resistance, lower dielectric constant, lower moisture absorption and improved adhesion and constantly being sought.
One method of lowering the moisture absorption characteristics of polyetherimide required in circuit board applications, is by incorporating silicones, preferably in the form of a silicone copolymer. It has been found, however, that although the resulting blend often has superior moisture absorption resistance, a significant decrease in heat distortion temperature (HDT) of the polyetherimide can be experienced, compared to the HDT of the polyetherimide free of silicone copolymer. In addition, if the silicone copolymer is not compatible or miscible with the polyetherimide, it will be hazy instead of clear, the blend also can show a low T.sub.g for the silicone copolymer and higher T.sub.g for the polyetherimide. It would be desirable, therefore, to be able to incorporate silicone copolymers into polyetherimide without experiencing a substantial reduction in the T.sub.g of the resulting blend compared to the initial polyetherimide T.sub.g.
The present invention is based on our discovery that certain silicone copolymers resulting from the intercondensation of aromatic bis(etheranhydride), phthalic anhydride-terminated polydiorganosiloxane and aryldiamine, as defined hereinafter, can be blended with polyetherimides, as defined hereinafter, to produce a blend of silicone copolymer and polyetherimide having a T.sub.g of at least 190.degree. C.